The invention relates to an apparatus for determination of a contact interval between a body contour and a movable object by spark discharge and more specifically to measuring plural intervals between plural contours of the body.
An apparatus of this type exhibiting a measurement and reference spark path is shown in German Patent Specification No. 3,513,799, especially in FIG. 2b thereof. An interval of distance to be maintained between a high voltage electrode directly connected to a body, a tool shank for example, and an object is determined and a follow-up or adjustment signal can be formed as a function of the interval for the purpose of a possible adjustment in the case of an interval deviation. If it were desired to monitor a plurality of intervals to be maintained between the body and the object, then by applying this principle, a plurality of such apparatus could be arranged juxtaposed. When monitoring two intervals, of distance for example, this arrangement would result in two electrode arrangements each comprising a measurement spark path and reference spark path provided in the measurement region. However, such arrangements would lead to considerable structure difficulties in view of the necessarily small dimensions of the electrode arrangements in the measurement regions and the likewise necessary physical proximity of the measurement spark path and the reference spark path.
Therefore, it is an object of the present invention to construct an apparatus of the type described above, so that a determination of at least two intervals of distance is possible therewith, without an appreciable increase in the overall volume.
This and other objects of the invention are attained by providing a unique electrode arrangement which allows measurement of a plurality of intervals of distance. A first and second high voltage electrode connected to a respective first and second pulse generator defines with a grounded object electrode a first and second measurement spark path, respectively, or with a grounded reference electrode, a first or second reference spark path, respectively for monitoring a first and second intervals of distance respectively. The grounded reference electrode may be a third electrode, or the first or second high voltage electrode may respectively serve as the reference electrode for the other high voltage electrode. A modulator alternately modulates the first and second pulse generators. A sensor is provided in circuit with the first and second reference spark paths for generating a modulation identifiable impulse when a spark discharge occurs along one of the first or second reference spark paths. An evaluation unit connected to the sensor determines from the impulses received from the sensors, which reference spark path in which a spark discharge occurred and generates an adjustment signal for the first or second interval. The modulation may be by amplitude pulse duration, polarity or time. The modulator may be, for example, an oscillator for driving the pulse generators which may include a transformer. When the high voltage electrodes act as reference electrodes for the other high voltage electrode, a switching circuit including a plurality of diodes is provided to effectuate this operation. To determine the symmetry or orthogonal of the system, a third electrode is provided having an equal distance with the first contour as the first high voltage electrode. A current source senses the current through the third electrode from the first pulse generator and the evaluation unit provides an appropriate third adjustment signal in response thereto.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.